1. Field of the Invention
The field of the invention is that of an automotive vehicle optical device, in particular an optical device for signaling and/or lighting, comprising a first luminous source and a light duct designed to conduct light originating from the first luminous source in the form of a beam with substantially parallel rays.
The subject of the invention is more particularly such an optical device in which the light duct comprises a rear face forming at least one reflecting facet designed to return some of the beam substantially along an optical axis of the light duct and a front face through which the light, after return by reflection on the facets, exits the light duct substantially along the optical axis.
Such solutions have already been developed to limit the amount of space required depth-wise along the optical axis.
2. Description of the Related Art
To ensure a signaling function, the document GB2320562A describes an optical device in which a collimator concentrates the light rays emitted by a luminous source, so that the beam with substantially parallel rays thus generated is directed into an entry face of a light duct in the form of a plate of small thickness, furnished with a plurality of reflecting facets. Through a front face of the light duct, the light rays exit the duct after having been returned by the facets. There are no dioptric elements adapted to the construction of a single beam of predetermined luminous distribution.
To ensure a lighting function of automotive vehicle headlight type, the document FR2514105A1 describes a similar solution, in which the optical device essentially comprises three functional assemblies: luminous flux concentration means, a light duct in the form of a unique transparent bar, and an add-on assembly of lenses attached forward, along the optical axis (direction of illumination), of the exit front face of the bar. The flux concentration assembly, arranged on the longitudinal axis of the bar, consists essentially of a luminous source and of an elliptical reflector or mirror. The luminous source consists of the filament or the arc of an automobile lamp. The lens assembly can be produced in the form of a unitary assembly forming the crystal of the headlight. The convergent lenses have axes substantially parallel to the direction of emission and are arranged in a relation of optical cooperation with reflecting facets (which are at the focus of the lenses) constituted by niches at the rear of the bar so that these lenses project in this direction, images corresponding to the facets.
These two known devices thus comprise a real luminous source, means for concentrating the luminous radiation issuing from this source onto the entry end of a light duct furnished with a plurality of reflecting facets forming as many virtual luminous sources and cooperating with a plurality of homologous dioptric elements so as to form an assembly of elementary beams merging into a single beam. By fitting the lenses outside the duct and optional hoods in the duct, on its own the device described in the document FR2514105A1 allows the construction of a single beam of predetermined luminous distribution, in particular a cutoff beam for a passing light for example.
But these solutions present the following main drawbacks:                high weight by reason of the use of lenses made of a material (glass) for withstanding the heat from the luminous sources,        significant complexity and cost, difficulty in obtaining and assembling, by reason of the number of parts used,        high aperture of the beams due to the presence of the lens assembly added forward of the front face of the duct,        tricky construction of a precise and highly efficient beam with predetermined luminous distribution,        necessity for relative centerings and positionings of the various constituent assemblies of the optical device,        difficulty in satisfying various possible functions to be carried out by the optical device,        mediocrity of style and of esthetic look.        
In the field of signaling, just as in that of lighting, numerous regulatory constraints leave little room to modify the look of the lights in the lit state, since the photometry of the light beams is imposed to a very broad extent. However, style and aesthetics are very significant data for this type of product, and automobile equipment manufacturers are seeking to give their products a “signature”, so that they are readily identifiable by the end user,